CN117353137A - Method and system for generating ultra-strong circular Airy laser pulse - Google Patents
Method and system for generating ultra-strong circular Airy laser pulse Download PDFInfo
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Abstract
The invention provides a method and a system for generating ultra-strong circular Airy laser pulses, comprising the following steps: determining a phase delay distribution function according to a Fourier transform approximation formula of the required circular Airy light near-field light intensity distribution; calculating a gray pattern corresponding to the phase delay distribution; carrying out experimental verification on the phase delay distribution gray pattern; preparing a phase plate according to the verified phase delay distribution gray pattern; and (3) constructing an experimental device for generating the circular ring Airy light by using the phase plate, and generating the ultra-strong circular ring Airy light laser pulse by modulating the output pulse of the ultra-strong femtosecond laser. The invention adopts the glass matrix phase plate with high damage threshold, and breaks through the limitation that the traditional method can only generate weak light strong circular Airy laser pulse due to low damage threshold of the liquid crystal spatial light modulator. The ultra-strong ring Airy laser pulse can be generated by a simple optical system, and the possibility is created for further application.
Description
Technical Field
The invention relates to the field of laser pulses, in particular to a method and a system for generating ultra-strong ring Airy laser pulses.
Background
In 2011, "Optics Letters", volume 36, phase 18, published "Fourier space generation of abruptly autofocusing beams and optical bottle beams", a method for generating circular ring airy is proposed, and circular ring airy is generated in the airspace through phase modulation of a gaussian beam and then a fourier transform process. The method is traditional and is also the most widely used method for generating circular blumea riparia. The device adopted in the phase modulation is a liquid crystal spatial light modulator, has a lower damage threshold and an effective modulation area, cannot be suitable for femtosecond laser with large energy and large spot size, and is limited in application.
The circular ring Airy light is the Airy light with axial rotation symmetry, and the propagation of the Airy light shows the known characteristics of the Airy light, namely, the main light intensity is greatly moved along a parabolic track due to no diffraction and transverse free acceleration, and the Airy light is anti-interference and self-healing after encountering obstacles. Meanwhile, the rotation symmetry of the propagation axis enables the laser to have long-distance controllable convergence performance, the initial laser pulse energy is distributed on a circular ring with a larger area through the regulation and control of the initial waveform, nonlinear loss of strong laser pulse propagation in the air is avoided, the laser is converged again in a designated long distance, and the super-strong light intensity is focused on the target body by means of the self-focusing phenomenon of strong light. Therefore, the laser beam is an ideal waveform for the long-distance propagation of the super-strong laser in a medium comprising the atmosphere and the like. Currently, circular ring airy light is mainly generated by modulating the gaussian light output by a laser with a spatial light modulator (spatial light modulator, SLM). Such a technical route is limited by the damage threshold of the spatial light modulator, especially for femtosecond laser pulses, the super-strong instantaneous power of which can lead to nonlinear response of the liquid crystal and reflective dielectric films and thus to ionization causing permanent damage. For a pulse of 800nm wavelength, which is a typical pulse width of several tens of femtoseconds, the damage threshold of the incident laser pulse energy is about 3mJ (pulse width 30 fs) when the beam cross section is about 10 mm. Such damage threshold severely limits the generation of ultra-fast, ultra-strong circular airy pulses. Therefore, there is a need to develop a new generation method of circular ring airy.
An optical geometric phase element design method for generating round Airy beam by complex amplitude modulation and a self-focusing lens device (CN 115598837A); the invention adopts an optical geometric phase element and a polarization filter, and directly generates circular ring Airy light through complex amplitude modulation, thereby avoiding the low utilization efficiency of the traditional Fourier transform method. However, the optical geometric phase element needs to be prepared by adopting a complex micro-nano processing technology, and the optical geometric phase element aiming at the femtosecond laser spot size is expensive in cost due to the large required size, which is not beneficial to practical application.
A system and method for generating terahertz waves by using a round Airy trichromatic field laser (CN 114389125A); the invention directly carries out phase modulation through the liquid crystal spatial light modulator to generate a circular ring light beam, the circular ring light beam also has the characteristic of circular ring self-focusing, is a similar light beam of circular ring Airy light, but is limited by the effective area of the spatial light modulator, and can not generate a circular ring light beam with a large initial radius, so that the self-focusing distance of the circular ring light beam is limited, and the generated circular ring Airy light energy is also limited by the damage threshold of the liquid crystal spatial light modulator, and can not generate circular ring Airy light femtosecond laser pulses with larger energy.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a method and a system for generating ultra-strong ring Airy laser pulses.
The method for generating the ultra-strong circular Airy laser pulse provided by the invention comprises the following steps of:
step S1: aiming at the circular ring Airy light pulse parameters to be generated, determining the near field light intensity distribution of the circular ring Airy light pulse parameters, and calculating a corresponding phase delay distribution function according to a Fourier transform approximation formula of the circular ring Airy light;
step S2: deriving as a phase delay gray pattern from the phase delay distribution function;
step S3: verifying the phase delay distribution gray pattern through experiments;
step S4: preparing a phase plate according to the verified phase delay distribution gray pattern;
step S5: and (3) constructing an experimental device for generating the circular ring Airy light by using the phase plate, and generating the ultra-strong circular ring Airy light laser pulse by modulating the output pulse of the ultra-strong femtosecond laser.
Preferably, in said step S1:
the required parameters include the initial radius r of the ring Airy light 0 A scale factor parameter w;
estimating the linear convergence distance f of Airy light by using the two parameters Ai The method comprises the following steps:
wherein lambda is the central wavelength of the femtosecond laser pulse;
meanwhile, a Fourier transform approximation formula of the ring Airy light is determined and expressed as an initial radius r of the ring 0 Function of scale factor parameter w:
wherein,for radial spatial frequency, f is the focal length of the Fourier lens, r is the radial coordinate, C 0 Is constant, a is the attenuation coefficient, +.>A Bessel function of the first class of 0 th order;
according to the requirement, in the phase delay distribution function calculated by the Fourier transform approximation formula of the near-field light intensity distribution of the circular Airy light, the phase delay distribution function is calculated by the formulaThe polar coordinates are converted into a Cartesian coordinate system, and x and y are the transverse and longitudinal coordinates in the Cartesian coordinate system, respectively.
Preferably, in said step S2:
the phase delay gray pattern is subjected to numerical discretization drawing according to the pixel number and the pixel size of the spatial light modulator; for the plotted phase-delayed gray pattern, gray values of 0 to 255 correspond to a phase delay of 0 to 2 pi.
Preferably, in said step S3:
the experiment verifies that the phase delay distribution gray pattern is performed by using an experimental device for generating circular ring Airy light through a spatial light modulator;
using a transmission type or reflection type spatial light modulator to load a phase delay distribution gray pattern to be verified into control software thereof to generate corresponding phase delay distribution, wherein the modulator is arranged on the front focal plane of the Fourier lens;
enabling the chirped amplified femtosecond laser to emit laser pulses, controlling the pulse energy to be smaller than the damage threshold of the spatial light modulator, and enabling the laser pulses to be incident to the spatial light modulator with specific phase delay distribution;
the modulator outputs light through a fourier lens;
placing a window sheet with a shielding object at a preset position in front of the back focal plane of the Fourier lens, completely shielding the intensity of the zero-order light which is not modulated, and generating the near-field light intensity distribution of the circular ring Airy light at the back focal plane of the lens;
the ring Ai Lifei seconds laser pulse freely propagates from the near field to the far field, after attenuation, the variation of the radius of the ring and the pulse light intensity along with the propagation distance is recorded and measured by a CCD camera, the focusing distance of the ring is determined, and the phase delay distribution function is verified compared with a preset design theoretical value.
Preferably, in said step S4:
verifying that the modulation area of the spatial light modulator used by the phase delay distribution function is different from the size of the phase plate to be prepared, and recalculating the phase delay distribution function according to the specific size of the phase plate;
the phase plate is made of optical glass, and 256-order quasi-continuous phase delay distribution preparation is completed by adopting a proper process according to a phase delay change function on the provided radius;
the specific preparation process depends on the manufacturer, including the liquid crystal beam-splitting DOE method.
Preferably, in said step S5:
enabling the super-strong femtosecond laser pulse to sequentially pass through a phase plate which is arranged on the front focal plane of the Fourier lens and has preset phase delay distribution, the Fourier lens and a window plate with a zero-order light shielding object, and generating circular Airy light near-field light intensity distribution on the rear focal plane of the Fourier lens;
the ultrastrong ring Ai Lifei seconds laser pulse freely propagates from the near field to the far field, after attenuation, the variation of the radius of the ring and the pulse light intensity along with the propagation distance is recorded and measured by a CCD camera on the light spot, and the focusing distance of the ring is determined and compared with a preset design theoretical value.
The invention provides a system for generating ultra-strong circular Airy laser pulse, which comprises:
module M1: aiming at the circular ring Airy light pulse parameters to be generated, determining the near field light intensity distribution of the circular ring Airy light pulse parameters, and calculating a corresponding phase delay distribution function according to a Fourier transform approximation formula of the circular ring Airy light;
module M2: deriving as a phase delay gray pattern from the phase delay distribution function;
module M3: verifying the phase delay distribution gray pattern through experiments;
module M4: preparing a phase plate according to the verified phase delay distribution gray pattern;
module M5: and (3) constructing an experimental device for generating the circular ring Airy light by using the phase plate, and generating the ultra-strong circular ring Airy light laser pulse by modulating the output pulse of the ultra-strong femtosecond laser.
Preferably, in said module M1:
the required parameters include the initial radius r of the ring Airy light 0 A scale factor parameter w;
estimating the linear convergence distance f of Airy light by using the two parameters Ai The method comprises the following steps:
wherein lambda is the central wavelength of the femtosecond laser pulse;
meanwhile, a Fourier transform approximation formula of the ring Airy light is determined and expressed as an initial radius r of the ring 0 Function of scale factor parameter w:
wherein,for radial spatial frequency, f is the focal length of the Fourier lens, r is the radial coordinate, C 0 Is constant, a is the attenuation coefficient, +.>A Bessel function of the first class of 0 th order;
according to the requirement, in the phase delay distribution function calculated by the Fourier transform approximation formula of the near-field light intensity distribution of the circular Airy light, the phase delay distribution function is calculated by the formulaConverting the polar coordinates into a Cartesian coordinate system, wherein x and y are respectively the transverse coordinates and the longitudinal coordinates in the Cartesian coordinate system;
in the module M2:
the phase delay gray pattern is subjected to numerical discretization drawing according to the pixel number and the pixel size of the spatial light modulator; for the plotted phase-delayed gray pattern, gray values of 0 to 255 correspond to a phase delay of 0 to 2 pi.
Preferably, in said module M3:
the experiment verifies that the phase delay distribution gray pattern is performed by using an experimental device for generating circular ring Airy light through a spatial light modulator;
using a transmission type or reflection type spatial light modulator to load a phase delay distribution gray pattern to be verified into control software thereof to generate corresponding phase delay distribution, wherein the modulator is arranged on the front focal plane of the Fourier lens;
enabling the chirped amplified femtosecond laser to emit laser pulses, controlling the pulse energy to be smaller than the damage threshold of the spatial light modulator, and enabling the laser pulses to be incident to the spatial light modulator with specific phase delay distribution;
the modulator outputs light through a fourier lens;
placing a window sheet with a shielding object at a preset position in front of the back focal plane of the Fourier lens, completely shielding the intensity of the zero-order light which is not modulated, and generating the near-field light intensity distribution of the circular ring Airy light at the back focal plane of the lens;
the ring Ai Lifei seconds laser pulse freely propagates from the near field to the far field, after attenuation, the variation of the radius of the ring and the pulse light intensity along with the propagation distance is recorded and measured by a CCD camera, the focusing distance of the ring is determined, and the phase delay distribution function is verified compared with a preset design theoretical value.
Preferably, in said module M4:
verifying that the modulation area of the spatial light modulator used by the phase delay distribution function is different from the size of the phase plate to be prepared, and recalculating the phase delay distribution function according to the specific size of the phase plate;
the phase plate is made of optical glass, and 256-order quasi-continuous phase delay distribution preparation is completed by adopting a proper process according to a phase delay change function on the provided radius;
the specific preparation process depends on manufacturers, including a liquid crystal beam splitting DOE method;
in the module M5:
enabling the super-strong femtosecond laser pulse to sequentially pass through a phase plate which is arranged on the front focal plane of the Fourier lens and has preset phase delay distribution, the Fourier lens and a window plate with a zero-order light shielding object, and generating circular Airy light near-field light intensity distribution on the rear focal plane of the Fourier lens;
the ultrastrong ring Ai Lifei seconds laser pulse freely propagates from the near field to the far field, after attenuation, the variation of the radius of the ring and the pulse light intensity along with the propagation distance is recorded and measured by a CCD camera on the light spot, and the focusing distance of the ring is determined and compared with a preset design theoretical value.
Compared with the prior art, the invention has the following beneficial effects:
1. compared with a liquid crystal spatial light modulator, the phase plate with specific phase delay distribution is prepared, and has higher damage threshold based on the optical glass material, and can adapt to femtosecond laser pulses with larger light spot size, so that ring Ai Lifei seconds laser pulses with larger energy can be generated;
2. aiming at the generation of the circular ring Airy light with specific requirements, the invention firstly utilizes the reflective liquid crystal spatial light modulator to obtain a required phase diagram generated by the circular ring Airy light through computer coding calculation, debugs the input test light, prepares a phase plate according to the corresponding phase delay distribution gray pattern after the debugging is successful, and reduces the trial-and-error cost of the phase plate preparation;
3. compared with the traditional low-energy circular ring Airy light generating device, the method and the device provided by the invention have the advantages that the optical path structure is simple and easy to realize, and the spatial light modulator is only required to be replaced by the prepared phase plate made of the optical glass material with specific phase delay distribution, so that the method and the device are very convenient in practical application.
Drawings
Other features, objects and advantages of the present invention will become more apparent upon reading of the detailed description of non-limiting embodiments, given with reference to the accompanying drawings in which:
FIG. 1 is a schematic diagram of an experimental apparatus for verifying a phase delay distribution gray pattern and applying a prepared phase plate, respectively;
FIG. 2 is a circular ring Airy light phase retardation gray pattern for use in an Airy light generation test of a liquid crystal spatial light modulator;
FIG. 3 is a circular ring Airy light phase retardation gray pattern for phase plate preparation;
fig. 4 shows the experimental results of the circular ring airy characterization generated by phase plate modulation: spot images of the ring airy at the fourier lens focal point (0 cm) and 100cm,150cm,230cm after the focal point, and the corresponding radial light intensity distribution.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the present invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications could be made by those skilled in the art without departing from the inventive concept. These are all within the scope of the present invention.
Example 1:
the invention provides a method and a device for generating ultra-strong ring Airy laser pulses; the chirped amplified femtosecond laser emits ultra-strong femtosecond laser pulses, and phase modulation required by generating circular ring Airy light is realized through a phase plate with preset phase delay distribution; the phase plate is made of optical glass, such as N-BK7 glass, and has extremely high damage threshold, phase delay distribution is calculated according to a Fourier transform approximate formula of circular Airy light, and is placed on the front focal plane of a Fourier lens after being processed and molded; the femtosecond laser pulse modulated by the phase plate realizes Fourier transform through the lens, forms near-field light intensity distribution of the circular ring Airy light on the back focal plane, and freely propagates after blocking zero-order light intensity; the focusing is carried out towards the axis at the distance determined by the near field, nonlinear self focusing is generated when the light intensity reaches the self focusing threshold value, the focusing of the light intensity is accelerated, and the super-strong light intensity is achieved at the designed and determined distance; the input laser pulse energy of the device is limited by the quality damage threshold of the phase sheet, and the incident femtosecond laser pulse with the beam section of about 10mm of the common optical glass can reach the damage threshold of the magnitude of 100mJ, which is improved by tens to hundreds times compared with the common spatial light modulator. Therefore, by adopting the method and the device provided by the invention, the ultra-strong circular Airy light femtosecond laser pulse can be generated only by a simple optical system, and the possibility is created for further application.
According to the method for generating ultra-strong circular Airy laser pulse provided by the invention, as shown in fig. 1-4, the method comprises the following steps:
step S1: aiming at the circular ring Airy light pulse parameters to be generated, determining the near field light intensity distribution of the circular ring Airy light pulse parameters, and calculating a corresponding phase delay distribution function according to a Fourier transform approximation formula of the circular ring Airy light;
specifically, in the step S1:
the required parameters include the initial radius r of the ring Airy light 0 A scale factor parameter w;
estimating the linear convergence distance f of Airy light by using the two parameters Ai The method comprises the following steps:
wherein lambda is the central wavelength of the femtosecond laser pulse;
meanwhile, a Fourier transform approximation formula of the ring Airy light is determined and expressed as an initial radius r of the ring 0 Function of scale factor parameter w:
wherein,for radial spatial frequency, f is the focal length of the Fourier lens, r is the radial coordinate, C 0 Is constant, a is the attenuation coefficient, +.>A Bessel function of the first class of 0 th order;
according to the requirement, in the phase delay distribution function calculated by the Fourier transform approximation formula of the near-field light intensity distribution of the circular Airy light, the phase delay distribution function is calculated by the formulaThe polar coordinates are converted into a Cartesian coordinate system, and x and y are the transverse and longitudinal coordinates in the Cartesian coordinate system, respectively.
Step S2: deriving as a phase delay gray pattern from the phase delay distribution function;
specifically, in the step S2:
the phase delay gray pattern is subjected to numerical discretization drawing according to the pixel number and the pixel size of the spatial light modulator; for the plotted phase-delayed gray pattern, gray values of 0 to 255 correspond to a phase delay of 0 to 2 pi.
Step S3: verifying the phase delay distribution gray pattern through experiments;
specifically, in the step S3:
the experiment verifies that the phase delay distribution gray pattern is performed by using an experimental device for generating circular ring Airy light through a spatial light modulator;
using a transmission type or reflection type spatial light modulator to load a phase delay distribution gray pattern to be verified into control software thereof to generate corresponding phase delay distribution, wherein the modulator is arranged on the front focal plane of the Fourier lens;
enabling the chirped amplified femtosecond laser to emit laser pulses, controlling the pulse energy to be smaller than the damage threshold of the spatial light modulator, and enabling the laser pulses to be incident to the spatial light modulator with specific phase delay distribution;
the modulator outputs light through a fourier lens;
placing a window sheet with a shielding object at a preset position in front of the back focal plane of the Fourier lens, completely shielding the intensity of the zero-order light which is not modulated, and generating the near-field light intensity distribution of the circular ring Airy light at the back focal plane of the lens;
the ring Ai Lifei seconds laser pulse freely propagates from the near field to the far field, after attenuation, the variation of the radius of the ring and the pulse light intensity along with the propagation distance is recorded and measured by a CCD camera, the focusing distance of the ring is determined, and the phase delay distribution function is verified compared with a preset design theoretical value.
Step S4: preparing a phase plate according to the verified phase delay distribution gray pattern;
specifically, in the step S4:
verifying that the modulation area of the spatial light modulator used by the phase delay distribution function is different from the size of the phase plate to be prepared, and recalculating the phase delay distribution function according to the specific size of the phase plate;
the phase plate is made of optical glass, and 256-order quasi-continuous phase delay distribution preparation is completed by adopting a proper process according to a phase delay change function on the provided radius;
the specific preparation process depends on the manufacturer, including the liquid crystal beam-splitting DOE method.
Step S5: and (3) constructing an experimental device for generating the circular ring Airy light by using the phase plate, and generating the ultra-strong circular ring Airy light laser pulse by modulating the output pulse of the ultra-strong femtosecond laser.
Specifically, in the step S5:
enabling the super-strong femtosecond laser pulse to sequentially pass through a phase plate which is arranged on the front focal plane of the Fourier lens and has preset phase delay distribution, the Fourier lens and a window plate with a zero-order light shielding object, and generating circular Airy light near-field light intensity distribution on the rear focal plane of the Fourier lens;
the ultrastrong ring Ai Lifei seconds laser pulse freely propagates from the near field to the far field, after attenuation, the variation of the radius of the ring and the pulse light intensity along with the propagation distance is recorded and measured by a CCD camera on the light spot, and the focusing distance of the ring is determined and compared with a preset design theoretical value.
Example 2:
example 2 is a preferable example of example 1 to more specifically explain the present invention.
The present invention also provides a system for generating ultra-strong ring airy laser pulses, which can be implemented by executing the flow steps of the method for generating ultra-strong ring airy laser pulses, i.e. the method for generating ultra-strong ring airy laser pulses can be understood by those skilled in the art as a preferred embodiment of the system for generating ultra-strong ring airy laser pulses.
The invention provides a system for generating ultra-strong circular Airy laser pulse, which comprises:
module M1: aiming at the circular ring Airy light pulse parameters to be generated, determining the near field light intensity distribution of the circular ring Airy light pulse parameters, and calculating a corresponding phase delay distribution function according to a Fourier transform approximation formula of the circular ring Airy light;
specifically, in the module M1:
the required parameters include the initial radius r of the ring Airy light 0 A scale factor parameter w;
estimating the linear convergence distance f of Airy light by using the two parameters Ai The method comprises the following steps:
wherein lambda is the central wavelength of the femtosecond laser pulse;
meanwhile, a Fourier transform approximation formula of the ring Airy light is determined and expressed as an initial radius r of the ring 0 Function of scale factor parameter w:
wherein,for radial spatial frequency, f is the focal length of the Fourier lens, r is the radial coordinate, C 0 Is constant, a is the attenuation coefficient, +.>A Bessel function of the first class of 0 th order;
according to the requirement, in the phase delay distribution function calculated by the Fourier transform approximation formula of the near-field light intensity distribution of the circular Airy light, the phase delay distribution function is calculated by the formulaConverting the polar coordinates into a Cartesian coordinate system, wherein x and y are respectively the transverse coordinates and the longitudinal coordinates in the Cartesian coordinate system;
module M2: deriving as a phase delay gray pattern from the phase delay distribution function;
in the module M2:
the phase delay gray pattern is subjected to numerical discretization drawing according to the pixel number and the pixel size of the spatial light modulator; for the plotted phase-delayed gray pattern, gray values of 0 to 255 correspond to a phase delay of 0 to 2 pi.
Module M3: verifying the phase delay distribution gray pattern through experiments;
specifically, in the module M3:
the experiment verifies that the phase delay distribution gray pattern is performed by using an experimental device for generating circular ring Airy light through a spatial light modulator;
using a transmission type or reflection type spatial light modulator to load a phase delay distribution gray pattern to be verified into control software thereof to generate corresponding phase delay distribution, wherein the modulator is arranged on the front focal plane of the Fourier lens;
enabling the chirped amplified femtosecond laser to emit laser pulses, controlling the pulse energy to be smaller than the damage threshold of the spatial light modulator, and enabling the laser pulses to be incident to the spatial light modulator with specific phase delay distribution;
the modulator outputs light through a fourier lens;
placing a window sheet with a shielding object at a preset position in front of the back focal plane of the Fourier lens, completely shielding the intensity of the zero-order light which is not modulated, and generating the near-field light intensity distribution of the circular ring Airy light at the back focal plane of the lens;
the ring Ai Lifei seconds laser pulse freely propagates from the near field to the far field, after attenuation, the variation of the radius of the ring and the pulse light intensity along with the propagation distance is recorded and measured by a CCD camera, the focusing distance of the ring is determined, and the phase delay distribution function is verified compared with a preset design theoretical value.
Module M4: preparing a phase plate according to the verified phase delay distribution gray pattern;
specifically, in the module M4:
verifying that the modulation area of the spatial light modulator used by the phase delay distribution function is different from the size of the phase plate to be prepared, and recalculating the phase delay distribution function according to the specific size of the phase plate;
the phase plate is made of optical glass, and 256-order quasi-continuous phase delay distribution preparation is completed by adopting a proper process according to a phase delay change function on the provided radius;
the specific preparation process depends on manufacturers, including a liquid crystal beam splitting DOE method;
module M5: and (3) constructing an experimental device for generating the circular ring Airy light by using the phase plate, and generating the ultra-strong circular ring Airy light laser pulse by modulating the output pulse of the ultra-strong femtosecond laser.
In the module M5:
enabling the super-strong femtosecond laser pulse to sequentially pass through a phase plate which is arranged on the front focal plane of the Fourier lens and has preset phase delay distribution, the Fourier lens and a window plate with a zero-order light shielding object, and generating circular Airy light near-field light intensity distribution on the rear focal plane of the Fourier lens;
the ultrastrong ring Ai Lifei seconds laser pulse freely propagates from the near field to the far field, after attenuation, the variation of the radius of the ring and the pulse light intensity along with the propagation distance is recorded and measured by a CCD camera on the light spot, and the focusing distance of the ring is determined and compared with a preset design theoretical value.
Example 3:
example 3 is a preferable example of example 1 to more specifically explain the present invention.
The invention provides a method and a device for generating ultra-strong ring Airy laser pulses, wherein an optimized embodiment of the method comprises the following steps and parameters:
(1) The initial radius r of the ring in this embodiment is determined according to the parameters of the desired generated ring Airy light 0 =2 mm, and the scale factor parameter w=0.2 mm.
(2) Calculating and designing the phase distribution of the liquid crystal spatial light modulator according to the Fourier transform approximation formula of the circular ring Airy light in the step 1, wherein the number of pixels of the liquid crystal spatial light modulator is 1920×1080, the size of the pixels is 8 μm, the radial spatial frequency k required in the calculation formula is calculated, the center wavelength of the femtosecond laser is lambda=800 nm, the focal length f of the Fourier lens is=2000 mm, the attenuation coefficient a=0.05, and C 0 =1. Equal proportion normalization of the phase delay distribution calculated according to the approximation formula to generate gray value distribution in [0,255]A gray scale image of a section, wherein a gray scale value 0 in the image represents a phase delay of 0, a gray scale value 255 represents a phase delay of 2pi, and a phase delay gray scale value pattern is shown in fig. 1.
(3) And (2) loading the calculated phase delay pattern to the reflective liquid crystal spatial light modulator.
(4) And 3, constructing an optical path required by the phase delay pattern test. The femto second laser pulse repetition frequency used in the test link is 10Hz, beam expansion is carried out, the adjustable aperture is adopted to limit the light spot size of the incident reflection type liquid crystal spatial light modulator so as to adapt to the effective modulation area of the spatial light modulator, the incident pulse energy is smaller than the damage threshold value, and the incident laser pulse energy of the experimental liquid crystal spatial light modulator is verified to be 3mJ.
(5) And 3, completing verification of the generated circular ring Airy light, wherein verification contents comprise pulse energy of the generated circular ring Airy light, an initial circular ring radius, a circular ring convergence distance and the like. The result showed that the energy of the pulse converted into airy pulse was 0.3mJ.
(6) After the validity of the phase pattern is determined in step 3, the phase delay pattern of the phase plate for generating the ring airy is recalculated. According to the requirement of the present embodiment, the phase plate size is set to 1 inch, and the phase delay pattern of the phase plate for generating the circular ring airy is as shown in fig. 2.
(7) According to the step 4, according to the recalculated phase delay distribution, a phase plate for generating the circular ring Airy light is prepared, the material of the phase plate is N-BK7 glass, the diameter of the phase plate is 1 inch, the number of pixels in the radial direction is 15000, and the phase plate presents 256-order quasi-continuous change phase delay.
(8) And 5, constructing a light path required by generating the circular Airy light according to the step 5. Wherein the phase plate is incident with a laser pulse energy of 20mJ.
(9) And 5, directly entering the circular ring Airy light after attenuation into a CCD camera to complete imaging. And (3) moving the position of the CCD camera, completing the space scanning from the initial state to the complete convergence of the circular ring Airy light, and completing the verification of the generated circular ring Airy light. The energy of the converted Airy light pulse was measured to be 1.3mJ. FIG. 3 is a spot image of circular Airy light at the focal point of the Fourier lens (0 cm) and 100cm,150cm,230cm after the focal point, and the corresponding radial intensity distribution.
Those skilled in the art will appreciate that the invention provides a system and its individual devices, modules, units, etc. that can be implemented entirely by logic programming of method steps, in addition to being implemented as pure computer readable program code, in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers, embedded microcontrollers, etc. Therefore, the system and various devices, modules and units thereof provided by the invention can be regarded as a hardware component, and the devices, modules and units for realizing various functions included in the system can also be regarded as structures in the hardware component; means, modules, and units for implementing the various functions may also be considered as either software modules for implementing the methods or structures within hardware components.
The foregoing describes specific embodiments of the present invention. It is to be understood that the invention is not limited to the particular embodiments described above, and that various changes or modifications may be made by those skilled in the art within the scope of the appended claims without affecting the spirit of the invention. The embodiments of the present application and features in the embodiments may be combined with each other arbitrarily without conflict.
Claims (10)
1. A method of generating ultra-strong ring airy laser pulses comprising:
step S1: aiming at the circular ring Airy light pulse parameters to be generated, determining the near field light intensity distribution of the circular ring Airy light pulse parameters, and calculating a corresponding phase delay distribution function according to a Fourier transform approximation formula of the circular ring Airy light;
step S2: deriving as a phase delay gray pattern from the phase delay distribution function;
step S3: verifying the phase delay distribution gray pattern through experiments;
step S4: preparing a phase plate according to the verified phase delay distribution gray pattern;
step S5: and (3) constructing an experimental device for generating the circular ring Airy light by using the phase plate, and generating the ultra-strong circular ring Airy light laser pulse by modulating the output pulse of the ultra-strong femtosecond laser.
2. The method of generating ultra-strong ring airy laser pulses according to claim 1, wherein in said step S1:
the required parameters include the initial radius r of the ring Airy light 0 A scale factor parameter w;
estimating the linear convergence distance f of Airy light by using the two parameters Ai The method comprises the following steps:
wherein lambda is the central wavelength of the femtosecond laser pulse;
meanwhile, a Fourier transform approximation formula of the ring Airy light is determined and expressed as an initial radius r of the ring 0 Function of scale factor parameter w:
wherein,for radial spatial frequency, f is the focal length of the Fourier lens, and r is the diameterCoordinates of directions, C 0 Is constant, a is the attenuation coefficient, +.>A Bessel function of the first class of 0 th order;
according to the requirement, in the phase delay distribution function calculated by the Fourier transform approximation formula of the near-field light intensity distribution of the circular Airy light, the phase delay distribution function is calculated by the formulaThe polar coordinates are converted into a Cartesian coordinate system, and x and y are the transverse and longitudinal coordinates in the Cartesian coordinate system, respectively.
3. The method of generating ultra-strong ring airy laser pulses according to claim 1, wherein in said step S2:
the phase delay gray pattern is subjected to numerical discretization drawing according to the pixel number and the pixel size of the spatial light modulator; for the plotted phase-delayed gray pattern, gray values of 0 to 255 correspond to a phase delay of 0 to 2 pi.
4. The method of generating ultra-strong ring airy laser pulses according to claim 1, wherein in said step S3:
the experiment verifies that the phase delay distribution gray pattern is performed by using an experimental device for generating circular ring Airy light through a spatial light modulator;
using a transmission type or reflection type spatial light modulator to load a phase delay distribution gray pattern to be verified into control software thereof to generate corresponding phase delay distribution, wherein the modulator is arranged on the front focal plane of the Fourier lens;
enabling the chirped amplified femtosecond laser to emit laser pulses, controlling the pulse energy to be smaller than the damage threshold of the spatial light modulator, and enabling the laser pulses to be incident to the spatial light modulator with specific phase delay distribution;
the modulator outputs light through a fourier lens;
placing a window sheet with a shielding object at a preset position in front of the back focal plane of the Fourier lens, completely shielding the intensity of the zero-order light which is not modulated, and generating the near-field light intensity distribution of the circular ring Airy light at the back focal plane of the lens;
the ring Ai Lifei seconds laser pulse freely propagates from the near field to the far field, after attenuation, the variation of the radius of the ring and the pulse light intensity along with the propagation distance is recorded and measured by a CCD camera, the focusing distance of the ring is determined, and the phase delay distribution function is verified compared with a preset design theoretical value.
5. The method of generating ultra-strong ring airy laser pulses according to claim 1, wherein in said step S4:
verifying that the modulation area of the spatial light modulator used by the phase delay distribution function is different from the size of the phase plate to be prepared, and recalculating the phase delay distribution function according to the specific size of the phase plate;
the phase plate is made of optical glass, and 256-order quasi-continuous phase delay distribution preparation is completed by adopting a preset proper process according to a phase delay change function on the provided radius;
the specific preparation process depends on the manufacturer, including the liquid crystal beam-splitting DOE method.
6. The method of generating ultra-strong ring airy laser pulses according to claim 1, wherein in said step S5:
enabling the super-strong femtosecond laser pulse to sequentially pass through a phase plate which is arranged on the front focal plane of the Fourier lens and has preset phase delay distribution, the Fourier lens and a window plate with a zero-order light shielding object, and generating circular Airy light near-field light intensity distribution on the rear focal plane of the Fourier lens;
the ultrastrong ring Ai Lifei seconds laser pulse freely propagates from the near field to the far field, after attenuation, the variation of the radius of the ring and the pulse light intensity along with the propagation distance is recorded and measured by a CCD camera on the light spot, and the focusing distance of the ring is determined and compared with a preset design theoretical value.
7. A system for generating ultra-strong ring airy laser pulses, comprising:
module M1: aiming at the circular ring Airy light pulse parameters to be generated, determining the near field light intensity distribution of the circular ring Airy light pulse parameters, and calculating a corresponding phase delay distribution function according to a Fourier transform approximation formula of the circular ring Airy light;
module M2: deriving as a phase delay gray pattern from the phase delay distribution function;
module M3: verifying the phase delay distribution gray pattern through experiments;
module M4: preparing a phase plate according to the verified phase delay distribution gray pattern;
module M5: and (3) constructing an experimental device for generating the circular ring Airy light by using the phase plate, and generating the ultra-strong circular ring Airy light laser pulse by modulating the output pulse of the ultra-strong femtosecond laser.
8. The system for generating ultra-strong ring airy laser pulses according to claim 7, wherein in said module M1:
the required parameters include the initial radius r of the ring Airy light 0 A scale factor parameter w;
estimating the linear convergence distance f of Airy light by using the two parameters Ai The method comprises the following steps:
wherein lambda is the central wavelength of the femtosecond laser pulse;
meanwhile, a Fourier transform approximation formula of the ring Airy light is determined and expressed as an initial radius r of the ring 0 Function of scale factor parameter w:
wherein,for radial spatial frequency, f is the focal length of the Fourier lens, r is the radial coordinate, C 0 Is constant, a is the attenuation coefficient, +.>A Bessel function of the first class of 0 th order;
according to the requirement, in the phase delay distribution function calculated by the Fourier transform approximation formula of the near-field light intensity distribution of the circular Airy light, the phase delay distribution function is calculated by the formulaConverting the polar coordinates into a Cartesian coordinate system, wherein x and y are respectively the transverse coordinates and the longitudinal coordinates in the Cartesian coordinate system;
in the module M2:
the phase delay gray pattern is subjected to numerical discretization drawing according to the pixel number and the pixel size of the spatial light modulator; for the plotted phase-delayed gray pattern, gray values of 0 to 255 correspond to a phase delay of 0 to 2 pi.
9. The system for generating ultra-strong ring airy laser pulses according to claim 7, wherein in said module M3:
the experiment verifies that the phase delay distribution gray pattern is performed by using an experimental device for generating circular ring Airy light through a spatial light modulator;
using a transmission type or reflection type spatial light modulator to load a phase delay distribution gray pattern to be verified into control software thereof to generate corresponding phase delay distribution, wherein the modulator is arranged on the front focal plane of the Fourier lens;
enabling the chirped amplified femtosecond laser to emit laser pulses, controlling the pulse energy to be smaller than the damage threshold of the spatial light modulator, and enabling the laser pulses to be incident to the spatial light modulator with specific phase delay distribution;
the modulator outputs light through a fourier lens;
placing a window sheet with a shielding object at a preset position in front of the back focal plane of the Fourier lens, completely shielding the intensity of the zero-order light which is not modulated, and generating the near-field light intensity distribution of the circular ring Airy light at the back focal plane of the lens;
the ring Ai Lifei seconds laser pulse freely propagates from the near field to the far field, after attenuation, the variation of the radius of the ring and the pulse light intensity along with the propagation distance is recorded and measured by a CCD camera, the focusing distance of the ring is determined, and the phase delay distribution function is verified compared with a preset design theoretical value.
10. The system for generating ultra-strong ring airy laser pulses according to claim 7, wherein:
in the module M4:
verifying that the modulation area of the spatial light modulator used by the phase delay distribution function is different from the size of the phase plate to be prepared, and recalculating the phase delay distribution function according to the specific size of the phase plate;
the phase plate is made of optical glass, and 256-order quasi-continuous phase delay distribution preparation is completed by adopting a preset proper process according to a phase delay change function on the provided radius;
the specific preparation process depends on manufacturers, including a liquid crystal beam splitting DOE method;
in the module M5:
enabling the super-strong femtosecond laser pulse to sequentially pass through a phase plate which is arranged on the front focal plane of the Fourier lens and has preset phase delay distribution, the Fourier lens and a window plate with a zero-order light shielding object, and generating circular Airy light near-field light intensity distribution on the rear focal plane of the Fourier lens;
the ultrastrong ring Ai Lifei seconds laser pulse freely propagates from the near field to the far field, after attenuation, the variation of the radius of the ring and the pulse light intensity along with the propagation distance is recorded and measured by a CCD camera on the light spot, and the focusing distance of the ring is determined and compared with a preset design theoretical value.
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